Under a superconducting phenomenon, a material exhibits complete demagnetization such that it develops no electric potential difference, i.e., its electrical resistance is reduced to zero although a finite stationary current flows in its interior. Accordingly, various applications of a superconductor have been proposed with respect to a transmission medium, an element or a device having absolutely no power loss.
Namely, a lot of fields of utilization, such as the electric power field of MHD power generation, power transmission, power storage and the like; the power field of a magnetic levitation train, an electromagnetic thruster equipment, and the like; and, further, supersensitive sensors for magnetic fields, microwaves and radioactive rays employed in the field of measurement of NMR, a .pi.-meson remedy apparatus, an experimentation apparatus for high energy physic and the like, can be listed as fields of applications of a superconductive material. Also in the field of electronics, it is expected as a technique which can implement a very high speed element of lower electric power consumption represented by a Josephson device.
On the other hand, as a superconductive oxide having a critical temperature Tc which is extremely higher than those of conventional metal system superconductive materials was discovered by Bednorz and Muller etc. in 1986, a possibility for high temperature superconduction has been greatly developed (Z. Phys. B64, 1986, September, pp. 189-193). A composite oxide system superconductive material discovered by Bednorz and Muller etc. has composition of [La, Ba].sub.2 CuO.sub.4 or [La, Sr].sub.2 CuO.sub.4, and is regarded as having a K.sub.2 NiF.sub.4 type crystal structure. While these materials are similar in crystal structure to generally known perovskite type composite oxide superconductive materials, their Tc, which are 30 to 50K, are extremely high as compared with the conventional superconductive materials. As to the generally known composite oxide system superconductive materials, a Ba--Pb--Bi system composite oxide disclosed in U.S. Pat. No. 3,932,315, and a Ba--Bi system composite oxide disclosed in Japanese Patent Laying-Open Gazette No. 60-173885 may be listed. However, Tc of these composite oxides are not more than 10K, and it has been indispensable to employ liquid helium (boiling point: 4.2K) for utilizing the same as superconductive materials.
The aforementioned [La, Ba].sub.2 CuO.sub.4 and the like, for example, include oxides of group IIa elements and group IIIa elements, and sintered bodies containing such oxides, which are regarded as having crystal structures similar to perovskite type oxides and may be called pseudo-perovskite type structures, can be divided broadly into a K.sub.2 NiF.sub.4 type oxide such as [La, Ba].sub.2 CuO.sub.4 or [La, Sr].sub.2 CuO.sub.4 etc., an orthorhombic type oxide of a Ba.sub.2 YCu.sub.3 O system, and an oxide containing Bi--Sr--Ca--Cu. These materials exhibit superconducting phenomenons at Tc which are extremely high as compared with the aforementioned generally known superconductive materials, and hence liquid hydrogen (boiling point: 20.4K), liquid neon (boiling point: 27.3K) or liquid nitrogen (boiling point: 77.3K) can be used as a cooling medium. Accordingly, expected are applications of these recently discovered composite oxide system superconductive materials having perovskite structures to transmission media for power or electric signals.
In general, products of oxides have been mainly produced by powder sintering, in which the oxides are molded into desired configurations by performing sintering after press molding or HIP molding etc. Also with respect to the aforementioned new superconductive oxides, therefore, merely bulk type sintered bodies are produced by a powder sintering method under existing circumstances, and substantially no attempts have been made in order to apply these oxides to practical electric transmission media, particularly as linear products.
To this end, the applicant has proposed a method of producing a superconducting elongated body comprising the steps of charging ceramics raw material powder composed of a composite oxide having a superconducting property in a metallic pipe, carrying out plastic deformation working for reducing the sectional area of the aforementioned metallic pipe in the state charged with the ceramic raw material powder, and heat treating the aforementioned metallic pipe after the plastic deformation, thereby sintering the aforementioned ceramic raw material powder charged in the aforementioned metallic pipe in Japanese Patent Application No. 63-025108 filed on Feb. 5, 1988 and entitled "Method of Producing Composite Oxide Ceramics System Superconducting Wire".
Although this method is a satisfactory method itself, skill is required for charging the raw material in the metallic pipe with sufficiently large bulk density since the raw material is charged in the metallic pipe in the form of powder, and hence it has been difficult to improve critical current density Jc if the state of charging is inferior.
According to the aforementioned method, further, the ceramic raw material powder is sintered in the metallic pipe, while it is difficult to control the crystal structure of a target superconductive material in this stage, and it is also difficult to thereafter provide appropriate orientativity to the crystal texture of the superconductive material existing in the metallic pipe. Also in such meaning, therefore, it has been impossible to expect high Jc for a superconductive material obtained by the aforementioned method using sintering.
In a method of charging powder in a similar metallic pipe and working the same into a wire, further, there is means for making orientation by stress through pressing or rolling, while it has been difficult to improve Jc in a thick film state if tape thickness is large, since the effect of the stress merely ranges over a limited thickness.
Accordingly, an object of the present invention is to provide a method of producing a superconducting wire rod having high critical current density Jc, which is provided with superconductivity by a ceramics system superconductive material.